Gas turbine engines, such as those which power aircraft and industrial equipment, employ a compressor section to compress air which is drawn into the engine and a turbine section to capture energy associated with the combustion of a fuel-air mixture which is exhausted from the engine's combustor section.
One or more cases are used to house the engine sections. For example, an engine case may house the turbine section. From the perspective of engine performance/efficiency, it is desirable to maintain as small a gap/clearance between the static engine case (stator) and the rotating turbine (rotor) blades as possible in order to maximize the energy that is captured by the turbine section as described above. However, a minimum clearance threshold must be maintained; otherwise, the turbine blades and the engine case may rub against one another so as to reduce the usable lifetime of the turbine blades or the engine case.
Active clearance control (ACC) algorithms are used to control the temperature of the engine case. For example, supplying cool air to the engine case causes the engine case to contract, thereby decreasing the clearance between the engine case and the turbine blades.